C++圖像輔助工具包Eigen入門代碼學習（很好的配合Opencv）

C++圖像輔助工具包Eigen入門代碼學習（很好的配合Opencv）

首先要說這個工具包非常的方便，解壓出來就可以用了。在工程裡面加入這個文件夾的路徑就可以了。

下面是一些代碼的練習：

#include   
#include   
using namespace Eigen;  
using namespace std;  
int main()  
{  

MatrixXd m = MatrixXd::Random(3,3);  
MatrixXd n;
 n=MatrixXd::Constant(3,3,1.2); //這是一個3*3的矩陣，裡面的值全部是1。2
 cout << "n =" << endl << n << endl; 
m = (m + MatrixXd::Constant(3,3,1.2)) * 50;  
cout << "m =" << endl << m << endl;  
VectorXd v(3);  
v << 1, 2, 3;  // 以下的結果說明是列向量3*1的。
cout << "m * v =" << endl << m * v << endl;  
return 0;

}  

下面會用到轉置：

#include   
#include   
using namespace Eigen;  
int main()  
{  

Matrix2d mat;  
mat << 1, 2,  
3, 4;  
Vector2d u(-1,1), v(2,0);  
std::cout << "Here is mat*mat:\n" << mat*mat << std::endl;  
std::cout << "Here is mat*u:\n" << mat*u << std::endl;  
std::cout << "Here is u^T*mat:\n" << u.transpose()*mat << std::endl;  //可以看出來.transpose()用來求轉置
std::cout << "Here is u^T*v:\n" << u.transpose()*v << std::endl;  
std::cout << "Here is u*v^T:\n" << u*v.transpose() << std::endl;  
std::cout << "Let's multiply mat by itself" << std::endl;  
mat = mat*mat;  
std::cout << "Now mat is mat:\n" << mat << std::endl;  

}  

#include   
#include   
using namespace std;  
int main()  
{  
Eigen::MatrixXf m(4,4);  
m << 1, 2, 3, 4,  
          5, 6, 7, 8,  
          9,10,11,12,  
          13,14,15,16;  
cout << "Block in the middle" << endl;  // 兩種不同的方式
cout << m.block<2,3>(1,1) << endl << endl;  
cout << "other kind Block in the middle" << endl;  
cout << m.block(1,1,2,3) << endl << endl;  
for (int i = 1; i <= 3; ++i)  
{  
cout << "Block of size " << i << "x" << i << endl;  
cout << m.block(0,0,i,i) << endl << endl;  
}  
}  

#include   
#include   
using namespace std;  
int main()  
{  
Eigen::ArrayXf v(6);  
v << 1, 2, 3, 4, 5, 6;  
cout << "v.head(3) =" << endl << v.head(3) << endl << endl;  
cout << "v.tail<3>() = " << endl << v.tail<3>() << endl << endl;  
v.segment(1,4) *= 2;  
cout << "after 'v.segment(1,4) *= 2', v =" << endl << v << endl; //這裡選出第2和第5個數來分別的*2 

Eigen::VectorXf v1(6);  //可以看出來是一樣的
v1 << 1 ,2 ,2 , 4, 5, 6;  
cout << "v1.head(3) =" << endl << v1.head(3) << endl << endl;  
cout << "v.tail<3>() = " << endl << v1.tail<3>() << endl << endl;  
v1.segment(1,4) *= 2;  
cout << "after 'v.segment(1,4) *= 2', v =" << endl << v1 << endl;  
} 

下來看一下基本的賦值情況：

#include 
#include 
#define SIZE 2

using namespace std;
using namespace Eigen;
void  main()
{
	MatrixXi m(SIZE,SIZE+1); // a (size)x(size+1)-matrix of int's
    cout<

下面的這張賦值方式：注意之間用的是逗號“ ，”

#include 
#include 
#define SIZE 2

using namespace std;
using namespace Eigen;
void  main()
{

int rows=5, cols=5;
MatrixXf m(rows,cols);
m << (Matrix3f() << 1, 2, 3, 4, 5, 6, 7, 8, 9).finished(),//不一樣的賦值方式e .finished() is used to get the actual matrix object once the comma initialization of our temporary submatrix is done. 
MatrixXf::Zero(3,cols-3),//用0來填補
MatrixXf::Zero(rows-3,3),
MatrixXf::Identity(rows-3,cols-3);//用單位矩陣來填補最下面的矩陣
cout << m<